Optical amplifier with a spectral gain monitor using a volume phase grating

Abstract

An optical amplifier system for amplifying an input wavelength division multiplexed (WDM) optical signal with a first optical coupler to extract a portion of the power of the input signal, an erbium-doped fiber amplifier to generate an output signal and a second optical coupler to extract a portion of the power of the output signal. A spectral monitoring unit having a volume phase grating separates the extracted input and output signals into spectral components. A photo-detector array of the spectral monitoring unit determines the power level of the spectral components. The system further includes a controller operative to control the operation of the amplifier in response to the power levels of the spectral components.

What is claimed is:  
     
       1. A system for amplifying an input wavelength division multiplexed (WDM) optical signal, the system comprising: 
       a first coupler configured to receive the input WDM optical signal and extract a portion therefrom;  
       a first spectral monitoring unit having a volume phase grating and optically connected to the first coupler, the first spectral monitoring unit configured to detect the power level of prescribed channels in the extracted portion of the input WDM optical signal;  
       an optical amplifier optically connected to the first coupler and configured to amplify the input WDM optical signal and generate an amplified output WDM optical signal;  
       a second coupler optically connected to the optical amplifier and configured to extract a portion of the output WDM optical signal therefrom;  
       a second spectral monitoring unit having a volume phase grating and optically connected to the second coupler, the second spectral monitoring unit configured to detect the power level of prescribed channels in the extracted portion of the output WDM optical signal; and  
       a controller electrically connected to the first spectral monitoring unit, the second spectral monitoring unit and the controller, the controller configured to receive the power levels in the prescribed channels in the extracted portions of the input and output signals and control the operation of the optical amplifier in response thereto.  
     
     
       2. The system of  claim 1  wherein the optical amplifier comprises an erbium-doped fiber and a laser pump source. 
     
     
       3. The system of  claim 1  wherein the first and second spectral monitoring units comprise: 
       an input fiber for receiving the optical signal;  
       a collimating lens in optical communication with the input fiber;  
       a volume phase grating in optical communication with the collimating lens, the volume phase grating configured to separate the optical signal from the focusing lens into the prescribed channels;  
       a focusing lens in optical communication with the volume phase grating; and  
       a photo-detector array in optical communication with the focusing lens, the photo-detector array configured to detect the power level of the prescribed channels transmitted through the focusing lens.  
     
     
       4. The system of  claim 3  wherein the photo-detector array has a plurality of photo-detectors positioned to detect the power level of the prescribed channels. 
     
     
       5. The system of  claim 1  wherein the controller is configured to control the amplification of input WDM signal in response to each of the prescribed channels. 
     
     
       6. A optical signal amplifier system for amplifying a wavelength division multiplexed (WDM) input signal, the amplifier system comprising: 
       a first optical coupler configured to receive the WDM input signal and extract a portion thereof;  
       an optical amplifier in optical communication with the first optical coupler and configured to amplify the WDM input signal and generate a WDM output signal;  
       a second optical coupler in optical communication with the optical amplifier, the second optical coupler configured to extract a portion of the WDM output signal;  
       a spectral monitoring unit in optical communication with the first optical coupler and the second optical coupler, the spectral monitoring unit having a volume phase grating and configured to determine the power level in prescribed channels of the extracted input and output WDM signals; and  
       a controller in electrical communication with the spectral monitoring unit and the optical amplifier, the controller configured to operate the optical amplifier in response to the power levels of the extracted input and output WDM signals.  
     
     
       7. The system of  claim 6  wherein the spectral monitoring unit is configured to determine the power levels in the prescribed channels of the extracted input and output WDM signals in a parallel manner. 
     
     
       8. The system of  claim 6  wherein the spectral monitoring unit is configured to determine the power levels in the prescribed channels of the extracted input and output WDM signals in a serial manner. 
     
     
       9. The system of  claim 6  wherein the spectral monitoring unit comprises: 
       a first input fiber for receiving the extracted input WDM signal;  
       a first collimating lens in optical communication with the first input fiber;  
       a second input fiber for receiving the extracted output WDM signal;  
       a second collimating lens in optical communication with the second input fiber;  
       a volume phase grating in optical communication with the first collimating lens and the second collimating lens, the volume phase grating configured to separate the extracted input and output WDM signals into prescribed channels;  
       a focusing lens in optical communication with the volume phase grating; and  
       a photo-detector array in optical communication with the focusing lens, the photo-detector array configured to detect the power level of each of the prescribed channels.  
     
     
       10. The system of  claim 9  wherein the photo-detector array comprises a plurality of photo-detectors, each of the photo-detectors configured to detect the power level of a respective one of the prescribed channels. 
     
     
       11. The system of  claim 6  further comprising an optical switch in optical communication with spectral monitoring unit, the extracted input WDM signal and the extracted output WDM signal, the optical switch configured to switch the input of the spectral monitoring unit between the extracted input WDM signal and the extracted output WDM signal. 
     
     
       12. The system of  claim 11  wherein the spectral monitoring unit comprises: 
       an input fiber for receiving the optical signal;  
       a collimating lens in optical communication with the input fiber;  
       a volume phase grating in optical communication with the collimating lens, the volume phase grating configured to separate the optical signal from the focusing lens into the prescribed channels;  
       a focusing lens in optical communication with the volume phase grating; and  
       a photo-detector array in optical communication with the focusing lens, the photo-detector array configured to detect the power level of respective ones of the prescribed channels transmitted through the focusing lens.  
     
     
       13. The system of  claim 12  wherein the optical switch is configured to switch between the extracted input WDM signal and the extracted output WDM signal by the controller. 
     
     
       14. A method of amplifying an input WDM optical signal with an optical amplifier system having a first and a second optical coupler, a first and a second spectral monitoring unit, an optical amplifier, and a controller, the method comprising the steps of: 
       a) extracting a portion of the input WDM optical signal with the first optical coupler;  
       b) separating the extracted portion of the input WDM optical signal into prescribed spectral components with the first spectral monitoring unit;  
       c) detecting the power level of each of the spectral components of the extracted input WDM optical signal with the first spectral monitoring unit;  
       d) amplifying the input WDM optical signal with the optical amplifier in order to generate an output WDM optical signal;  
       e) extracting a portion of the output WDM optical signal with the second optical coupler;  
       f) separating the extracted portion of the output WDM optical signal into prescribed spectral components with the second spectral monitoring unit;  
       g) detecting the power level of each of the spectral components of the extracted output WDM optical signal with the second spectral monitoring unit; and  
       h) controlling the optical amplifier with the controller in response to the power levels of the spectral components of the extracted input WDM optical signal and the extracted output WDM optical signal.  
     
     
       15. The method of  claim 14  wherein the first spectral monitoring unit comprises a volume phase grating and step (b) comprises separating the extracted portion of the input WDM optical signal into prescribed spectral components with the volume phase grating. 
     
     
       16. The method of  claim 14  wherein the second spectral monitoring unit comprises a volume phase grating and step (f) comprises separating the extracted portion of the input WDM optical signal into prescribed spectral components with the volume phase grating. 
     
     
       17. The method of  claim 14  wherein the first spectral monitoring unit comprises a photo-detector array and step (c) comprises detecting the power level of each of the prescribed spectral components with the photo-detector array. 
     
     
       18. The method of  claim 17  wherein the photo-detector array comprises a plurality of photo-detectors operative to detect the power level of a respective one of the spectral components and step (c) comprises detecting the power level of each prescribed spectral component with a respective one of the photo-detectors. 
     
     
       19. The method of  claim 14  wherein the second spectral monitoring unit comprises a photo-detector array and step (g) comprises detecting the power level of each of the prescribed spectral components with the photo-detector array. 
     
     
       20. The method of  claim 19  wherein the photo-detector array comprises a plurality of photo detectors operative to detect the power level of a respective one of the spectral components and step (c) comprises detecting the power level of each prescribed spectral component with a respective one of the photo-detectors. 
     
     
       21. The method of  claim 14  wherein in step (a) the first optical coupler extracts about 2% of the power of the input WDM optical signal. 
     
     
       22. The method of  claim 14  wherein in step (e) the second optical coupler extracts about 2% of the power of the output WDM optical signal. 
     
     
       23. The method of  claim 14  wherein the optical amplifier is a laser pump source in optical communication with an erbium-doped fiber and step (d) comprises amplifying the input WDM optical signal with the erbium-doped fiber and laser pump source. 
     
     
       24. A method of amplifying an input WDM optical signal with an optical amplifier system having a first and a second optical coupler, a spectral monitoring unit, an optical amplifier and a controller, the method comprising the steps of: 
       a) extracting a portion of the input WDM optical signal with the first optical coupler;  
       b) amplifying the input WDM optical signal with the optical amplifier in order to generate an output WDM optical signal;  
       c) extracting a portion of the output WDM optical signal with the second optical coupler,  
       e) separating the extracted portion of the input WDM optical signal and the extracted portion of the output WDM optical signal into respective spectral components with the spectral monitoring unit;  
       f) detecting the power level of the spectral components with the spectral monitoring unit; and  
       g) controlling the amplification of the input WDM optical signal with the optical amplifier and the controller in response to the power level of the spectral components detected by the spectral monitoring unit.  
     
     
       25. The method of  claim 24  wherein the optical amplifier has a laser pump source and an erbium-doped fiber and step (b) comprises amplifying the input WDM optical signal with the laser pump source and the erbium-doped fiber. 
     
     
       26. The method of  claim 24  wherein the spectral monitoring unit comprises a volume phase grating and step (e) comprises separating the extracted portion of the input WDM optical signal and the extracted portion of the output WDM optical signal with the volume phase grating. 
     
     
       27. The method of  claim 24  wherein the spectral monitoring unit comprises a photo-detector array and step (f) comprises detecting the power level of the spectral components with the photo-detector array. 
     
     
       28. The method of  claim 27  wherein the photo-detector array has a plurality of photo-detectors corresponding to the spectral components and step (f) comprises detecting the power level of each of the spectral components with a respective one of the photo-detectors. 
     
     
       29. The method of  claim 24  wherein in step (a) the first optical coupler extracts about 2% of the power of the input WDM optical signal. 
     
     
       30. The method of  claim 24  wherein in step (c) the second optical coupler extracts about 2% of the power of the output WDM optical signal. 
     
     
       31. The method of  claim 24  wherein the spectral monitoring unit has an optical switch and a volume phase grating and step (e) comprises switching between the input WDM optical signal and the output WDM optical signal with the optical switch in order to separate the spectral components with the volume phase grating. 
     
     
       32. An optical amplifier system for amplifying a wavelength division multiplexed (WDM) optical signal, the system comprising: 
       first coupling means for extracting a portion of the input WDM optical signal;  
       first monitoring means having a volume phase grating for detecting the power level of spectral components of the extracted input WDM optical signal;  
       amplifying means for amplifying the input WDM optical signal and generating an amplified output WDM optical signal;  
       second coupling means for extracting a portion of the output WDM optical signal;  
       second monitoring means having a volume phase grating for detecting the power level of spectral components of the extracted output WDM optical signal; and  
       control means for controlling the operation of the amplifying means in response to the power level of the spectral components of the extracted input WDM optical signal and the extracted output WDM optical signal.  
     
     
       33. The system of  claim 32  wherein the first coupling means and the second coupling means are respective first and second optical couplers. 
     
     
       34. The system of  claim 32  wherein the first monitoring means and the second monitoring means are respective first and second spectral monitoring units. 
     
     
       35. The system of  claim 32  wherein the amplifying means is a laser pump source and an erbium-doped fiber. 
     
     
       36. A system for amplifying an input optical signal, the system comprising: 
       first coupling means for extracting a portion of the power of the input optical signal;  
       amplifying means for amplifying the input optical signal;  
       second coupling means for extracting a portion of the power of the output optical signal;  
       monitoring means having a volume phase grating for separating spectral components of the extracted input and output optical signals and determining the power level of the spectral components; and  
       control means for controlling the operation of the amplifying means in response to the power level of the spectral components.  
     
     
       37. The system of  claim 36  wherein the first and second coupling means are respective first and second optical couplers. 
     
     
       38. The system of  claim 36  wherein the monitoring means is a spectral monitoring unit. 
     
     
       39. The system of  claim 36  wherein the amplifying means is a laser pump source and an erbium-doped fiber.